1. Field of the Invention
This invention relates generally to automatically controlled musical instruments and specifically to a musical pitch control apparatus for each of a plurality of musical strings of a stringed musical instrument.
2. Discussion of the Related Art
A number of proposals for automatic tuning devices appear in the literature, but these have not been widely accepted. Clark U.S. Pat. No. 2,624,027 employs a motor control system to tension a vibrating filament. Scholz U.S. Pats. Nos. 4,375,180 and 4,426,907 describe an automatic self-tuning device for guitars, using electrical contacts that make or break to energize an electric motor that controls the string tension. Skinn et al. U.S. Pat. No. 4,803,908 describes a digital tuning system in which each string of a guitar has an associated tuning arm and stepper motor. A transducer senses the pitch of the vibrating strings and adjusts the string tensions accordingly. Murata et al. U.S. Pat. No. 4,928,563 relates to an electronic tuning apparatus for electric guitars in which pitch information is extracted from the instrument during playing, and a small motor is energized for each string to adjust the string tension.
Zacaroli U.S. Pat. No. 5,095,797 discloses an automatic tuning control arrangement for a stringed musical instrument comprising a pivoted tone arm, a pivot, a length memory metal alloy wire traction motor, a strain sensor means, a current driving circuit, and a biasing means for applying a spring bias in opposition to the musical string tension. Several improvements to Zacaroli '797 have been made: the spring bias is applied in a direction that opposes a shortening of the alloy wire, a specific embodiment of the current driving circuit is disclosed, a lamp indicating a pitch threshold is taught, a shut-down safety feature is incorporated to deactivate one of the current driving circuits in the event that the associated musical string breaks, and a plurality of pulleys are utilized to reduce an area occupied by the apparatus.